1. Field of the Invention
The present invention relates to focus adjusting apparatus and particularly to a focus adjusting apparatus for use in an image sensing apparatus such as a video camera having an optical system provided with focus lens means including a lens member formed of a polymer gel substance having electro-reactive deformability.
2. Description of the Prior Art
Conventionally, focus adjustment in an image sensing apparatus such as a video camera is effected by moving a plurality of lenses by a motor. Such a conventional focus adjusting apparatus is disclosed for example in Japanese Patent Publication No. 10814/1986.
However, such a conventional focus adjusting apparatus requires complicated mechanisms for moving plural lenses and a motor as a power source and, therefore, the apparatus can not be made to have a small size and a light weight and in addition it consumes a large quantity of electric power.
On the other hand, focus adjusting apparatus using liquid crystal as a lens material have been proposed. One of such apparatus is disclosed in U.S. Pat. No. 4,037,929, which indicates a technique for changing a focal distance without deforming the lens, utilizing a property of liquid crystal that its refractive index changes dependent on application of control voltage. However, according to this technique, the refractive index n of the liquid crystal lens is changed only by .DELTA.n=0.2 or so at the maximum and the focal distance can not be reduced sufficiently. In other words, it is theoretically possible to manufacture a focus adjusting apparatus using a liquid crystal lens but difficulties are involved in practically realizing such apparatus because it is necessary to change the refractive index to a large extent.
Further, a focus adjusting apparatus using piezo ceramic as a lens material has been proposed as in U.S. Pat. No. 3,614,456. According to this patent, a thin cylindrical piezo ceramic in a container expands due to application of control voltage and the liquid in the container is pressurized to cause a thin film at the opening of the container to curve like a convex lens, whereby a lens is formed. However, a range of contraction or expansion due to voltage applied to the piezo ceramic is only from several tens of .mu.m to about 100 .mu.m at most and it is considered to be difficult for the thin film to form, by the deformation of such extent, a lens enabling an in-focus condition. Accordingly, although it is also theoretically possible to manufacture a focus adjusting apparatus using a lens making use of deformation of piezo ceramic, much difficulty will be involved in practically realizing such apparatus.